The filming of Francis Ford Coppola's Apocalypse Now lasted a hellish 16 months, while Stanley Kubrick's final work, the Cruise-Kidman psychodrama Eyes Wide Shut, clocks into the Guinness World Records for "the longest constant movie shoot", at 400 days. But the British director Michael Winterbottom (24 Hour Party People, 9 Songs, The Trip) has just surpassed even these two masters of the sado-masochistic movie marathon. His latest film, a one-off drama for Channel 4, was five years in the making.

Well, it was and it wasn't. For half a decade, Winterbottom and two of his regular actors, John Simm and Shirley Henderson, took a few weeks out of their busy schedules to make Everyday, which looks at the effects of a five-year prison sentence on a family from rural Norfolk. Unfolding in real time, the drama is largely improvised, with Simm (Life on Mars, State of Play) and Henderson (who worked with Winterbottom on Wonderland, 24 Hour Party People and A Cock and Bull Story) performing with a real family of four children – the Kirks – in the Kirks' home and in real prisons. The resulting drama has a poetic realism reminiscent of Ken Loach at his best.

"A lot of films take place over a period of time," says Winterbottom. "But when you're making fictional films you tend to shoot over seven or eight weeks, which means you're dealing with quite conventional ways of showing time passing – make up, or in the case of children, taking different children to play the same part. I thought it would be interesting to have a fictional story, but allow the film to take place over a real period of time."

Cast and crew filmed twice a year – often around Christmas because that tended to be an easy time to catch everyone – then summer for contrast, the children growing up in front of our eyes. "The film is about duration," says Winterbottom, one of Britain's most varied and innovative film-makers. "I didn't want it to be about crime and punishment; I wanted it to be about separation."

Simm, who plays Ian, a husband and father locked up for an unspecified crime, says that the project became part of his life. "We'd all just get a phone-call when coming back from a job, and if we were all around, I'd go back to prison."

Filming took place at a number of jails, with inmates and wardens playing themselves. "I would interact with real prisoners," says Simm. "I got on with everyone I came into contact with. But then I'd swagger down the prison corridor and suddenly you'd get, 'Get back in your time-machine, knob-head'...

"Michael wanted me to spend a night in the cell… that didn't happen. It's very claustrophobic in there – and the prisoners all said that the one thing you remember throughout the whole sentence is when the door shuts for the first time in your cell."

In one respect Simm, who has an 11-year-old son, Ryan, and a five-year-old daughter, Molly, with actress Kate Magowan, didn't need to use his imagination. "That thing about being away and missing your kids is something I can relate to," he says. "It's nothing like being in prison, but I sometimes spend three months away and I'm used to those phone-calls and how upsetting it is – 'I missed this' and 'I missed that' – and they send little videos of their first day at school…"

Prison visits were filmed in the real visiting rooms, with real wardens working the room. "They were policing visits as they normally do," says Winterbottom. "It's quite hard to know what you are allowed to do and what you're not allowed to do, so it was great to have genuine people there. But prison visiting rooms are not the most enticing places."

Indeed, there is an uncomfortable scene where one of the younger Kirk children, Sean, starts bawling his eyes out. Acting, improvisation, or for real? "It is a weird area about how much is acting and how much is not," says Winterbottom. "When Sean burst into tears it would be spontaneous – we hadn't asked him to. But then although he'd have to do it exactly the same again, he found himself hitting the same area of tears each time."

Simm, Henderson and the children went for days out to the seaside to get to know each other, while on the first day of filming, Henderson arrived early at their house to wake them up (scenes that are included at the beginning of the film). And Simm says that his separation from the children just added to the sense of realism. "Sometimes I wouldn't see them for a whole year," he says. "I'd be at the end of a phone, with Shirley, doing the Christmas thing – and we always had a real conversation because they're kind of not acting; it's their real names, their real house. I'd ask what they got for Christmas and it was really what they got for Christmas."

Winterbottom chose to film in north Norfolk partly because he has "a little place" there, and shot A Cock and Bull Story in the county and knows it well, but also because the famous big skies and beaches (especially the vast Holkham beach, which also appears at the end of Shakespeare in Love) accentuated the sense of Ian's confinement. "Also I think that any time you have a story set in prison it tends to be urban – and I liked the idea that this was a rural story," he says. "The casting director looked around schools in north Norfolk – we were looking for one child – and then when we saw the Kirks, we thought brilliant, because more is better." Has he inspired the children to want to become actors? "I hope not," says Winterbottom , as quick as a flash. "They were coming round to it," adds Simm. "By the end they were correcting us on continuity."